The caldarium (hot room) had a hot water bath, known as alveus, in the rear, and a basin of cold water to the left.

The ingenious system of hypocaustum (under-floor heating) made it possible to carry heat to the caldarium (hot room) and tepidarium (warm room).

There was a chamber of isolated air in the wall at the rear of the alveus, in order to prevent heat from escaping, which consisted of ceramic pegs fastened to the brick wall.